/**
 * @file
 * Address Resolution Protocol module for IP over Ethernet
 *
 * Functionally, ARP is divided into two parts. The first maps an IP address
 * to a physical address when sending a packet, and the second part answers
 * requests from other machines for our physical address.
 *
 * This implementation complies with RFC 826 (Ethernet ARP). It supports
 * Gratuitious ARP from RFC3220 (IP Mobility Support for IPv4) section 4.6
 * if an interface calls etharp_gratuitous(our_netif) upon address change.
 */

/*
 * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
 * Copyright (c) 2003-2004 Leon Woestenberg <leon.woestenberg@axon.tv>
 * Copyright (c) 2003-2004 Axon Digital Design B.V., The Netherlands.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 */

#include "lwip/opt.h"

#if LWIP_ARP /* don't build if not configured for use in lwipopts.h */

#include "lwip/inet.h"
#include "lwip/ip.h"
#include "lwip/stats.h"
#include "lwip/snmp.h"
#include "lwip/dhcp.h"
#include "lwip/autoip.h"
#include "netif/etharp.h"

#if PPPOE_SUPPORT
	#include "netif/ppp_oe.h"
#endif /* PPPOE_SUPPORT */

#include <string.h>

/** the time an ARP entry stays valid after its last update,
 *  for ARP_TMR_INTERVAL = 5000, this is
 *  (240 * 5) seconds = 20 minutes.
 */
#define ARP_MAXAGE 240
/** the time an ARP entry stays pending after first request,
 *  for ARP_TMR_INTERVAL = 5000, this is
 *  (2 * 5) seconds = 10 seconds.
 *
 *  @internal Keep this number at least 2, otherwise it might
 *  run out instantly if the timeout occurs directly after a request.
 */
#define ARP_MAXPENDING 2

#define HWTYPE_ETHERNET 1

#define ARPH_HWLEN(hdr) (ntohs((hdr)->_hwlen_protolen) >> 8)
#define ARPH_PROTOLEN(hdr) (ntohs((hdr)->_hwlen_protolen) & 0xff)

#define ARPH_HWLEN_SET(hdr, len) (hdr)->_hwlen_protolen = htons(ARPH_PROTOLEN(hdr) | ((len) << 8))
#define ARPH_PROTOLEN_SET(hdr, len) (hdr)->_hwlen_protolen = htons((len) | (ARPH_HWLEN(hdr) << 8))

enum etharp_state {
	ETHARP_STATE_EMPTY = 0,
	ETHARP_STATE_PENDING,
	ETHARP_STATE_STABLE
};

struct etharp_entry {
#if ARP_QUEUEING
	/**
	 * Pointer to queue of pending outgoing packets on this ARP entry.
	 */
	struct etharp_q_entry* q;
#endif
	struct ip_addr ipaddr;
	struct eth_addr ethaddr;
	enum etharp_state state;
	u8_t ctime;
	struct netif* netif;
};

const struct eth_addr ethbroadcast = {{0xff, 0xff, 0xff, 0xff, 0xff, 0xff}};
const struct eth_addr ethzero = {{0, 0, 0, 0, 0, 0}};
static struct etharp_entry arp_table[ARP_TABLE_SIZE];
#if !LWIP_NETIF_HWADDRHINT
	static u8_t etharp_cached_entry;
#endif

/**
 * Try hard to create a new entry - we want the IP address to appear in
 * the cache (even if this means removing an active entry or so). */
#define ETHARP_TRY_HARD 1
#define ETHARP_FIND_ONLY  2

#if LWIP_NETIF_HWADDRHINT
#define NETIF_SET_HINT(netif, hint)  if (((netif) != NULL) && ((netif)->addr_hint != NULL))  \
                                      *((netif)->addr_hint) = (hint);
static s8_t find_entry(struct ip_addr* ipaddr, u8_t flags, struct netif* netif);
#else /* LWIP_NETIF_HWADDRHINT */
static s8_t find_entry(struct ip_addr* ipaddr, u8_t flags);
#endif /* LWIP_NETIF_HWADDRHINT */

static err_t update_arp_entry(struct netif* netif, struct ip_addr* ipaddr, struct eth_addr* ethaddr, u8_t flags);


/* Some checks, instead of etharp_init(): */
#if (LWIP_ARP && (ARP_TABLE_SIZE > 0x7f))
	#error "If you want to use ARP, ARP_TABLE_SIZE must fit in an s8_t, so, you have to reduce it in your lwipopts.h"
#endif


#if ARP_QUEUEING
/**
 * Free a complete queue of etharp entries
 *
 * @param q a qeueue of etharp_q_entry's to free
 */
static void
free_etharp_q(struct etharp_q_entry* q)
{
	struct etharp_q_entry* r;
	LWIP_ASSERT("q != NULL", q != NULL);
	LWIP_ASSERT("q->p != NULL", q->p != NULL);

	while(q) {
		r = q;
		q = q->next;
		LWIP_ASSERT("r->p != NULL", (r->p != NULL));
		pbuf_free(r->p);
		memp_free(MEMP_ARP_QUEUE, r);
	}
}
#endif

/**
 * Clears expired entries in the ARP table.
 *
 * This function should be called every ETHARP_TMR_INTERVAL microseconds (5 seconds),
 * in order to expire entries in the ARP table.
 */
void
etharp_tmr(void)
{
	u8_t i;

	LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer\n"));

	/* remove expired entries from the ARP table */
	for(i = 0; i < ARP_TABLE_SIZE; ++i) {
		arp_table[i].ctime++;

		if(((arp_table[i].state == ETHARP_STATE_STABLE) &&
		        (arp_table[i].ctime >= ARP_MAXAGE)) ||
		        ((arp_table[i].state == ETHARP_STATE_PENDING)  &&
		         (arp_table[i].ctime >= ARP_MAXPENDING))) {
			/* pending or stable entry has become old! */
			LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired %s entry %"U16_F".\n",
			                           arp_table[i].state == ETHARP_STATE_STABLE ? "stable" : "pending", (u16_t)i));
			/* clean up entries that have just been expired */
			/* remove from SNMP ARP index tree */
			snmp_delete_arpidx_tree(arp_table[i].netif, &arp_table[i].ipaddr);
#if ARP_QUEUEING

			/* and empty packet queue */
			if(arp_table[i].q != NULL) {
				/* remove all queued packets */
				LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: freeing entry %"U16_F", packet queue %p.\n", (u16_t)i, (void*)(arp_table[i].q)));
				free_etharp_q(arp_table[i].q);
				arp_table[i].q = NULL;
			}

#endif
			/* recycle entry for re-use */
			arp_table[i].state = ETHARP_STATE_EMPTY;
		}

#if ARP_QUEUEING

		/* still pending entry? (not expired) */
		if(arp_table[i].state == ETHARP_STATE_PENDING) {
			/* resend an ARP query here? */
		}

#endif
	}
}

/**
 * Search the ARP table for a matching or new entry.
 *
 * If an IP address is given, return a pending or stable ARP entry that matches
 * the address. If no match is found, create a new entry with this address set,
 * but in state ETHARP_EMPTY. The caller must check and possibly change the
 * state of the returned entry.
 *
 * If ipaddr is NULL, return a initialized new entry in state ETHARP_EMPTY.
 *
 * In all cases, attempt to create new entries from an empty entry. If no
 * empty entries are available and ETHARP_TRY_HARD flag is set, recycle
 * old entries. Heuristic choose the least important entry for recycling.
 *
 * @param ipaddr IP address to find in ARP cache, or to add if not found.
 * @param flags
 * - ETHARP_TRY_HARD: Try hard to create a entry by allowing recycling of
 * active (stable or pending) entries.
 *
 * @return The ARP entry index that matched or is created, ERR_MEM if no
 * entry is found or could be recycled.
 */
static s8_t
#if LWIP_NETIF_HWADDRHINT
	find_entry(struct ip_addr* ipaddr, u8_t flags, struct netif* netif)
#else /* LWIP_NETIF_HWADDRHINT */
	find_entry(struct ip_addr* ipaddr, u8_t flags)
#endif /* LWIP_NETIF_HWADDRHINT */
{
	s8_t old_pending = ARP_TABLE_SIZE, old_stable = ARP_TABLE_SIZE;
	s8_t empty = ARP_TABLE_SIZE;
	u8_t i = 0, age_pending = 0, age_stable = 0;
#if ARP_QUEUEING
	/* oldest entry with packets on queue */
	s8_t old_queue = ARP_TABLE_SIZE;
	/* its age */
	u8_t age_queue = 0;
#endif

	/* First, test if the last call to this function asked for the
	 * same address. If so, we're really fast! */
	if(ipaddr) {
		/* ipaddr to search for was given */
#if LWIP_NETIF_HWADDRHINT
		if((netif != NULL) && (netif->addr_hint != NULL)) {
			/* per-pcb cached entry was given */
			u8_t per_pcb_cache = *(netif->addr_hint);

			if((per_pcb_cache < ARP_TABLE_SIZE) && arp_table[per_pcb_cache].state == ETHARP_STATE_STABLE) {
				/* the per-pcb-cached entry is stable */
				if(ip_addr_cmp(ipaddr, &arp_table[per_pcb_cache].ipaddr)) {
					/* per-pcb cached entry was the right one! */
					ETHARP_STATS_INC(etharp.cachehit);
					return per_pcb_cache;
				}
			}
		}

#else /* #if LWIP_NETIF_HWADDRHINT */

		if(arp_table[etharp_cached_entry].state == ETHARP_STATE_STABLE) {
			/* the cached entry is stable */
			if(ip_addr_cmp(ipaddr, &arp_table[etharp_cached_entry].ipaddr)) {
				/* cached entry was the right one! */
				ETHARP_STATS_INC(etharp.cachehit);
				return etharp_cached_entry;
			}
		}

#endif /* #if LWIP_NETIF_HWADDRHINT */
	}

	/**
	 * a) do a search through the cache, remember candidates
	 * b) select candidate entry
	 * c) create new entry
	 */

	/* a) in a single search sweep, do all of this
	 * 1) remember the first empty entry (if any)
	 * 2) remember the oldest stable entry (if any)
	 * 3) remember the oldest pending entry without queued packets (if any)
	 * 4) remember the oldest pending entry with queued packets (if any)
	 * 5) search for a matching IP entry, either pending or stable
	 *    until 5 matches, or all entries are searched for.
	 */

	for(i = 0; i < ARP_TABLE_SIZE; ++i) {
		/* no empty entry found yet and now we do find one? */
		if((empty == ARP_TABLE_SIZE) && (arp_table[i].state == ETHARP_STATE_EMPTY)) {
			LWIP_DEBUGF(ETHARP_DEBUG, ("find_entry: found empty entry %"U16_F"\n", (u16_t)i));
			/* remember first empty entry */
			empty = i;
		}
		/* pending entry? */
		else if(arp_table[i].state == ETHARP_STATE_PENDING) {
			/* if given, does IP address match IP address in ARP entry? */
			if(ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
				LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: found matching pending entry %"U16_F"\n", (u16_t)i));
				/* found exact IP address match, simply bail out */
#if LWIP_NETIF_HWADDRHINT
				NETIF_SET_HINT(netif, i);
#else /* #if LWIP_NETIF_HWADDRHINT */
				etharp_cached_entry = i;
#endif /* #if LWIP_NETIF_HWADDRHINT */
				return i;
#if ARP_QUEUEING
				/* pending with queued packets? */
			} else if(arp_table[i].q != NULL) {
				if(arp_table[i].ctime >= age_queue) {
					old_queue = i;
					age_queue = arp_table[i].ctime;
				}

#endif
				/* pending without queued packets? */
			} else {
				if(arp_table[i].ctime >= age_pending) {
					old_pending = i;
					age_pending = arp_table[i].ctime;
				}
			}
		}
		/* stable entry? */
		else if(arp_table[i].state == ETHARP_STATE_STABLE) {
			/* if given, does IP address match IP address in ARP entry? */
			if(ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
				LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: found matching stable entry %"U16_F"\n", (u16_t)i));
				/* found exact IP address match, simply bail out */
#if LWIP_NETIF_HWADDRHINT
				NETIF_SET_HINT(netif, i);
#else /* #if LWIP_NETIF_HWADDRHINT */
				etharp_cached_entry = i;
#endif /* #if LWIP_NETIF_HWADDRHINT */
				return i;
				/* remember entry with oldest stable entry in oldest, its age in maxtime */
			} else if(arp_table[i].ctime >= age_stable) {
				old_stable = i;
				age_stable = arp_table[i].ctime;
			}
		}
	}

	/* { we have no match } => try to create a new entry */

	/* no empty entry found and not allowed to recycle? */
	if(((empty == ARP_TABLE_SIZE) && ((flags & ETHARP_TRY_HARD) == 0))
	        /* or don't create new entry, only search? */
	        || ((flags & ETHARP_FIND_ONLY) != 0)) {
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: no empty entry found and not allowed to recycle\n"));
		return (s8_t)ERR_MEM;
	}

	/* b) choose the least destructive entry to recycle:
	 * 1) empty entry
	 * 2) oldest stable entry
	 * 3) oldest pending entry without queued packets
	 * 4) oldest pending entry with queued packets
	 *
	 * { ETHARP_TRY_HARD is set at this point }
	 */

	/* 1) empty entry available? */
	if(empty < ARP_TABLE_SIZE) {
		i = empty;
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting empty entry %"U16_F"\n", (u16_t)i));
	}
	/* 2) found recyclable stable entry? */
	else if(old_stable < ARP_TABLE_SIZE) {
		/* recycle oldest stable*/
		i = old_stable;
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest stable entry %"U16_F"\n", (u16_t)i));
#if ARP_QUEUEING
		/* no queued packets should exist on stable entries */
		LWIP_ASSERT("arp_table[i].q == NULL", arp_table[i].q == NULL);
#endif
		/* 3) found recyclable pending entry without queued packets? */
	} else if(old_pending < ARP_TABLE_SIZE) {
		/* recycle oldest pending */
		i = old_pending;
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest pending entry %"U16_F" (without queue)\n", (u16_t)i));
#if ARP_QUEUEING
		/* 4) found recyclable pending entry with queued packets? */
	} else if(old_queue < ARP_TABLE_SIZE) {
		/* recycle oldest pending */
		i = old_queue;
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest pending entry %"U16_F", freeing packet queue %p\n", (u16_t)i, (void*)(arp_table[i].q)));
		free_etharp_q(arp_table[i].q);
		arp_table[i].q = NULL;
#endif
		/* no empty or recyclable entries found */
	} else {
		return (s8_t)ERR_MEM;
	}

	/* { empty or recyclable entry found } */
	LWIP_ASSERT("i < ARP_TABLE_SIZE", i < ARP_TABLE_SIZE);

	if(arp_table[i].state != ETHARP_STATE_EMPTY) {
		snmp_delete_arpidx_tree(arp_table[i].netif, &arp_table[i].ipaddr);
	}

	/* recycle entry (no-op for an already empty entry) */
	arp_table[i].state = ETHARP_STATE_EMPTY;

	/* IP address given? */
	if(ipaddr != NULL) {
		/* set IP address */
		ip_addr_set(&arp_table[i].ipaddr, ipaddr);
	}

	arp_table[i].ctime = 0;
#if LWIP_NETIF_HWADDRHINT
	NETIF_SET_HINT(netif, i);
#else /* #if LWIP_NETIF_HWADDRHINT */
	etharp_cached_entry = i;
#endif /* #if LWIP_NETIF_HWADDRHINT */
	return (err_t)i;
}

/**
 * Send an IP packet on the network using netif->linkoutput
 * The ethernet header is filled in before sending.
 *
 * @params netif the lwIP network interface on which to send the packet
 * @params p the packet to send, p->payload pointing to the (uninitialized) ethernet header
 * @params src the source MAC address to be copied into the ethernet header
 * @params dst the destination MAC address to be copied into the ethernet header
 * @return ERR_OK if the packet was sent, any other err_t on failure
 */
static err_t
etharp_send_ip(struct netif* netif, struct pbuf* p, struct eth_addr* src, struct eth_addr* dst)
{
	struct eth_hdr* ethhdr = p->payload;
	u8_t k;

	LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
	            (netif->hwaddr_len == ETHARP_HWADDR_LEN));
	k = ETHARP_HWADDR_LEN;

	while(k > 0) {
		k--;
		ethhdr->dest.addr[k] = dst->addr[k];
		ethhdr->src.addr[k]  = src->addr[k];
	}

	ethhdr->type = htons(ETHTYPE_IP);
	LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_send_ip: sending packet %p\n", (void*)p));
	/* send the packet */
	return netif->linkoutput(netif, p);
}

/**
 * Update (or insert) a IP/MAC address pair in the ARP cache.
 *
 * If a pending entry is resolved, any queued packets will be sent
 * at this point.
 *
 * @param ipaddr IP address of the inserted ARP entry.
 * @param ethaddr Ethernet address of the inserted ARP entry.
 * @param flags Defines behaviour:
 * - ETHARP_TRY_HARD Allows ARP to insert this as a new item. If not specified,
 * only existing ARP entries will be updated.
 *
 * @return
 * - ERR_OK Succesfully updated ARP cache.
 * - ERR_MEM If we could not add a new ARP entry when ETHARP_TRY_HARD was set.
 * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
 *
 * @see pbuf_free()
 */
static err_t
update_arp_entry(struct netif* netif, struct ip_addr* ipaddr, struct eth_addr* ethaddr, u8_t flags)
{
	s8_t i;
	u8_t k;
	LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry()\n"));
	LWIP_ASSERT("netif->hwaddr_len == ETHARP_HWADDR_LEN", netif->hwaddr_len == ETHARP_HWADDR_LEN);
	LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: %"U16_F".%"U16_F".%"U16_F".%"U16_F" - %02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F"\n",
	            ip4_addr1(ipaddr), ip4_addr2(ipaddr), ip4_addr3(ipaddr), ip4_addr4(ipaddr),
	            ethaddr->addr[0], ethaddr->addr[1], ethaddr->addr[2],
	            ethaddr->addr[3], ethaddr->addr[4], ethaddr->addr[5]));

	/* non-unicast address? */
	if(ip_addr_isany(ipaddr) ||
	        ip_addr_isbroadcast(ipaddr, netif) ||
	        ip_addr_ismulticast(ipaddr)) {
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: will not add non-unicast IP address to ARP cache\n"));
		return ERR_ARG;
	}

	/* find or create ARP entry */
#if LWIP_NETIF_HWADDRHINT
	i = find_entry(ipaddr, flags, netif);
#else /* LWIP_NETIF_HWADDRHINT */
	i = find_entry(ipaddr, flags);
#endif /* LWIP_NETIF_HWADDRHINT */

	/* bail out if no entry could be found */
	if(i < 0)
		return (err_t)i;

	/* mark it stable */
	arp_table[i].state = ETHARP_STATE_STABLE;
	/* record network interface */
	arp_table[i].netif = netif;

	/* insert in SNMP ARP index tree */
	snmp_insert_arpidx_tree(netif, &arp_table[i].ipaddr);

	LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: updating stable entry %"S16_F"\n", (s16_t)i));
	/* update address */
	k = ETHARP_HWADDR_LEN;

	while(k > 0) {
		k--;
		arp_table[i].ethaddr.addr[k] = ethaddr->addr[k];
	}

	/* reset time stamp */
	arp_table[i].ctime = 0;
#if ARP_QUEUEING

	/* this is where we will send out queued packets! */
	while(arp_table[i].q != NULL) {
		struct pbuf* p;
		/* remember remainder of queue */
		struct etharp_q_entry* q = arp_table[i].q;
		/* pop first item off the queue */
		arp_table[i].q = q->next;
		/* get the packet pointer */
		p = q->p;
		/* now queue entry can be freed */
		memp_free(MEMP_ARP_QUEUE, q);
		/* send the queued IP packet */
		etharp_send_ip(netif, p, (struct eth_addr*)(netif->hwaddr), ethaddr);
		/* free the queued IP packet */
		pbuf_free(p);
	}

#endif
	return ERR_OK;
}

/**
 * Finds (stable) ethernet/IP address pair from ARP table
 * using interface and IP address index.
 * @note the addresses in the ARP table are in network order!
 *
 * @param netif points to interface index
 * @param ipaddr points to the (network order) IP address index
 * @param eth_ret points to return pointer
 * @param ip_ret points to return pointer
 * @return table index if found, -1 otherwise
 */
s8_t
etharp_find_addr(struct netif* netif, struct ip_addr* ipaddr,
                 struct eth_addr** eth_ret, struct ip_addr** ip_ret)
{
	s8_t i;

	LWIP_UNUSED_ARG(netif);

#if LWIP_NETIF_HWADDRHINT
	i = find_entry(ipaddr, ETHARP_FIND_ONLY, NULL);
#else /* LWIP_NETIF_HWADDRHINT */
	i = find_entry(ipaddr, ETHARP_FIND_ONLY);
#endif /* LWIP_NETIF_HWADDRHINT */

	if((i >= 0) && arp_table[i].state == ETHARP_STATE_STABLE) {
		*eth_ret = &arp_table[i].ethaddr;
		*ip_ret = &arp_table[i].ipaddr;
		return i;
	}

	return -1;
}

/**
 * Updates the ARP table using the given IP packet.
 *
 * Uses the incoming IP packet's source address to update the
 * ARP cache for the local network. The function does not alter
 * or free the packet. This function must be called before the
 * packet p is passed to the IP layer.
 *
 * @param netif The lwIP network interface on which the IP packet pbuf arrived.
 * @param p The IP packet that arrived on netif.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
void
etharp_ip_input(struct netif* netif, struct pbuf* p)
{
	struct eth_hdr* ethhdr;
	struct ip_hdr* iphdr;
	LWIP_ERROR("netif != NULL", (netif != NULL), return;);
	/* Only insert an entry if the source IP address of the
	   incoming IP packet comes from a host on the local network. */
	ethhdr = p->payload;
	iphdr = (struct ip_hdr*)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
#if ETHARP_SUPPORT_VLAN

	if(ethhdr->type == ETHTYPE_VLAN) {
		iphdr = (struct ip_hdr*)((u8_t*)ethhdr + SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR);
	}

#endif /* ETHARP_SUPPORT_VLAN */

	/* source is not on the local network? */
	if(!ip_addr_netcmp(&(iphdr->src), &(netif->ip_addr), &(netif->netmask))) {
		/* do nothing */
		return;
	}

	LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_ip_input: updating ETHARP table.\n"));
	/* update ARP table */
	/* @todo We could use ETHARP_TRY_HARD if we think we are going to talk
	 * back soon (for example, if the destination IP address is ours. */
	update_arp_entry(netif, &(iphdr->src), &(ethhdr->src), 0);
}


/**
 * Responds to ARP requests to us. Upon ARP replies to us, add entry to cache
 * send out queued IP packets. Updates cache with snooped address pairs.
 *
 * Should be called for incoming ARP packets. The pbuf in the argument
 * is freed by this function.
 *
 * @param netif The lwIP network interface on which the ARP packet pbuf arrived.
 * @param ethaddr Ethernet address of netif.
 * @param p The ARP packet that arrived on netif. Is freed by this function.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
void
etharp_arp_input(struct netif* netif, struct eth_addr* ethaddr, struct pbuf* p)
{
	struct etharp_hdr* hdr;
	struct eth_hdr* ethhdr;
	/* these are aligned properly, whereas the ARP header fields might not be */
	struct ip_addr sipaddr, dipaddr;
	u8_t i;
	u8_t for_us;
#if LWIP_AUTOIP
	const u8_t* ethdst_hwaddr;
#endif /* LWIP_AUTOIP */

	LWIP_ERROR("netif != NULL", (netif != NULL), return;);

	/* drop short ARP packets: we have to check for p->len instead of p->tot_len here
	   since a struct etharp_hdr is pointed to p->payload, so it musn't be chained! */
	if(p->len < SIZEOF_ETHARP_PACKET) {
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
		            ("etharp_arp_input: packet dropped, too short (%"S16_F"/%"S16_F")\n", p->tot_len,
		             (s16_t)SIZEOF_ETHARP_PACKET));
		ETHARP_STATS_INC(etharp.lenerr);
		ETHARP_STATS_INC(etharp.drop);
		pbuf_free(p);
		return;
	}

	ethhdr = p->payload;
	hdr = (struct etharp_hdr*)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
#if ETHARP_SUPPORT_VLAN

	if(ethhdr->type == ETHTYPE_VLAN) {
		hdr = (struct etharp_hdr*)(((u8_t*)ethhdr) + SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR);
	}

#endif /* ETHARP_SUPPORT_VLAN */

	/* RFC 826 "Packet Reception": */
	if((hdr->hwtype != htons(HWTYPE_ETHERNET)) ||
	        (hdr->_hwlen_protolen != htons((ETHARP_HWADDR_LEN << 8) | sizeof(struct ip_addr))) ||
	        (hdr->proto != htons(ETHTYPE_IP)) ||
	        (ethhdr->type != htons(ETHTYPE_ARP)))  {
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
		            ("etharp_arp_input: packet dropped, wrong hw type, hwlen, proto, protolen or ethernet type (%"U16_F"/%"U16_F"/%"U16_F"/%"U16_F"/%"U16_F")\n",
		             hdr->hwtype, ARPH_HWLEN(hdr), hdr->proto, ARPH_PROTOLEN(hdr), ethhdr->type));
		ETHARP_STATS_INC(etharp.proterr);
		ETHARP_STATS_INC(etharp.drop);
		pbuf_free(p);
		return;
	}

	ETHARP_STATS_INC(etharp.recv);

#if LWIP_AUTOIP
	/* We have to check if a host already has configured our random
	 * created link local address and continously check if there is
	 * a host with this IP-address so we can detect collisions */
	autoip_arp_reply(netif, hdr);
#endif /* LWIP_AUTOIP */

	/* Copy struct ip_addr2 to aligned ip_addr, to support compilers without
	 * structure packing (not using structure copy which breaks strict-aliasing rules). */
	SMEMCPY(&sipaddr, &hdr->sipaddr, sizeof(sipaddr));
	SMEMCPY(&dipaddr, &hdr->dipaddr, sizeof(dipaddr));

	/* this interface is not configured? */
	if(netif->ip_addr.addr == 0) {
		for_us = 0;
	} else {
		/* ARP packet directed to us? */
		for_us = ip_addr_cmp(&dipaddr, &(netif->ip_addr));
	}

	/* ARP message directed to us? */
	if(for_us) {
		/* add IP address in ARP cache; assume requester wants to talk to us.
		 * can result in directly sending the queued packets for this host. */
		update_arp_entry(netif, &sipaddr, &(hdr->shwaddr), ETHARP_TRY_HARD);
		/* ARP message not directed to us? */
	} else {
		/* update the source IP address in the cache, if present */
		update_arp_entry(netif, &sipaddr, &(hdr->shwaddr), 0);
	}

	/* now act on the message itself */
	switch(htons(hdr->opcode)) {
		/* ARP request? */
		case ARP_REQUEST:
			/* ARP request. If it asked for our address, we send out a
			 * reply. In any case, we time-stamp any existing ARP entry,
			 * and possiby send out an IP packet that was queued on it. */

			LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: incoming ARP request\n"));

			/* ARP request for our address? */
			if(for_us) {

				LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: replying to ARP request for our IP address\n"));
				/* Re-use pbuf to send ARP reply.
				   Since we are re-using an existing pbuf, we can't call etharp_raw since
				   that would allocate a new pbuf. */
				hdr->opcode = htons(ARP_REPLY);

				hdr->dipaddr = hdr->sipaddr;
				SMEMCPY(&hdr->sipaddr, &netif->ip_addr, sizeof(hdr->sipaddr));

				LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
				            (netif->hwaddr_len == ETHARP_HWADDR_LEN));
				i = ETHARP_HWADDR_LEN;
#if LWIP_AUTOIP
				/* If we are using Link-Local, ARP packets must be broadcast on the
				 * link layer. (See RFC3927 Section 2.5) */
				ethdst_hwaddr = ((netif->autoip != NULL) && (netif->autoip->state != AUTOIP_STATE_OFF)) ? (u8_t*)(ethbroadcast.addr) : hdr->shwaddr.addr;
#endif /* LWIP_AUTOIP */

				while(i > 0) {
					i--;
					hdr->dhwaddr.addr[i] = hdr->shwaddr.addr[i];
#if LWIP_AUTOIP
					ethhdr->dest.addr[i] = ethdst_hwaddr[i];
#else  /* LWIP_AUTOIP */
					ethhdr->dest.addr[i] = hdr->shwaddr.addr[i];
#endif /* LWIP_AUTOIP */
					hdr->shwaddr.addr[i] = ethaddr->addr[i];
					ethhdr->src.addr[i] = ethaddr->addr[i];
				}

				/* hwtype, hwaddr_len, proto, protolen and the type in the ethernet header
				   are already correct, we tested that before */

				/* return ARP reply */
				netif->linkoutput(netif, p);
				/* we are not configured? */
			} else if(netif->ip_addr.addr == 0) {
				/* { for_us == 0 and netif->ip_addr.addr == 0 } */
				LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: we are unconfigured, ARP request ignored.\n"));
				/* request was not directed to us */
			} else {
				/* { for_us == 0 and netif->ip_addr.addr != 0 } */
				LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: ARP request was not for us.\n"));
			}

			break;

		case ARP_REPLY:
			/* ARP reply. We already updated the ARP cache earlier. */
			LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: incoming ARP reply\n"));
#if (LWIP_DHCP && DHCP_DOES_ARP_CHECK)
			/* DHCP wants to know about ARP replies from any host with an
			 * IP address also offered to us by the DHCP server. We do not
			 * want to take a duplicate IP address on a single network.
			 * @todo How should we handle redundant (fail-over) interfaces? */
			dhcp_arp_reply(netif, &sipaddr);
#endif
			break;

		default:
			LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: ARP unknown opcode type %"S16_F"\n", htons(hdr->opcode)));
			ETHARP_STATS_INC(etharp.err);
			break;
	}

	/* free ARP packet */
	pbuf_free(p);
}

/**
 * Resolve and fill-in Ethernet address header for outgoing IP packet.
 *
 * For IP multicast and broadcast, corresponding Ethernet addresses
 * are selected and the packet is transmitted on the link.
 *
 * For unicast addresses, the packet is submitted to etharp_query(). In
 * case the IP address is outside the local network, the IP address of
 * the gateway is used.
 *
 * @param netif The lwIP network interface which the IP packet will be sent on.
 * @param q The pbuf(s) containing the IP packet to be sent.
 * @param ipaddr The IP address of the packet destination.
 *
 * @return
 * - ERR_RTE No route to destination (no gateway to external networks),
 * or the return type of either etharp_query() or etharp_send_ip().
 */
err_t
etharp_output(struct netif* netif, struct pbuf* q, struct ip_addr* ipaddr)
{
	struct eth_addr* dest, mcastaddr;

	/* make room for Ethernet header - should not fail */
	if(pbuf_header(q, sizeof(struct eth_hdr)) != 0) {
		/* bail out */
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
		            ("etharp_output: could not allocate room for header.\n"));
		LINK_STATS_INC(link.lenerr);
		return ERR_BUF;
	}

	/* assume unresolved Ethernet address */
	dest = NULL;
	/* Determine on destination hardware address. Broadcasts and multicasts
	 * are special, other IP addresses are looked up in the ARP table. */

	/* broadcast destination IP address? */
	if(ip_addr_isbroadcast(ipaddr, netif)) {
		/* broadcast on Ethernet also */
		dest = (struct eth_addr*)&ethbroadcast;
		/* multicast destination IP address? */
	} else if(ip_addr_ismulticast(ipaddr)) {
		/* Hash IP multicast address to MAC address.*/
		mcastaddr.addr[0] = 0x01;
		mcastaddr.addr[1] = 0x00;
		mcastaddr.addr[2] = 0x5e;
		mcastaddr.addr[3] = ip4_addr2(ipaddr) & 0x7f;
		mcastaddr.addr[4] = ip4_addr3(ipaddr);
		mcastaddr.addr[5] = ip4_addr4(ipaddr);
		/* destination Ethernet address is multicast */
		dest = &mcastaddr;
		/* unicast destination IP address? */
	} else {
		/* outside local network? */
		if(!ip_addr_netcmp(ipaddr, &(netif->ip_addr), &(netif->netmask))) {
			/* interface has default gateway? */
			if(netif->gw.addr != 0) {
				/* send to hardware address of default gateway IP address */
				ipaddr = &(netif->gw);
				/* no default gateway available */
			} else {
				/* no route to destination error (default gateway missing) */
				return ERR_RTE;
			}
		}

		/* queue on destination Ethernet address belonging to ipaddr */
		return etharp_query(netif, ipaddr, q);
	}

	/* continuation for multicast/broadcast destinations */
	/* obtain source Ethernet address of the given interface */
	/* send packet directly on the link */
	return etharp_send_ip(netif, q, (struct eth_addr*)(netif->hwaddr), dest);
}

/**
 * Send an ARP request for the given IP address and/or queue a packet.
 *
 * If the IP address was not yet in the cache, a pending ARP cache entry
 * is added and an ARP request is sent for the given address. The packet
 * is queued on this entry.
 *
 * If the IP address was already pending in the cache, a new ARP request
 * is sent for the given address. The packet is queued on this entry.
 *
 * If the IP address was already stable in the cache, and a packet is
 * given, it is directly sent and no ARP request is sent out.
 *
 * If the IP address was already stable in the cache, and no packet is
 * given, an ARP request is sent out.
 *
 * @param netif The lwIP network interface on which ipaddr
 * must be queried for.
 * @param ipaddr The IP address to be resolved.
 * @param q If non-NULL, a pbuf that must be delivered to the IP address.
 * q is not freed by this function.
 *
 * @note q must only be ONE packet, not a packet queue!
 *
 * @return
 * - ERR_BUF Could not make room for Ethernet header.
 * - ERR_MEM Hardware address unknown, and no more ARP entries available
 *   to query for address or queue the packet.
 * - ERR_MEM Could not queue packet due to memory shortage.
 * - ERR_RTE No route to destination (no gateway to external networks).
 * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
 *
 */
err_t
etharp_query(struct netif* netif, struct ip_addr* ipaddr, struct pbuf* q)
{
	struct eth_addr* srcaddr = (struct eth_addr*)netif->hwaddr;
	err_t result = ERR_MEM;
	s8_t i; /* ARP entry index */

	/* non-unicast address? */
	if(ip_addr_isbroadcast(ipaddr, netif) ||
	        ip_addr_ismulticast(ipaddr) ||
	        ip_addr_isany(ipaddr)) {
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: will not add non-unicast IP address to ARP cache\n"));
		return ERR_ARG;
	}

	/* find entry in ARP cache, ask to create entry if queueing packet */
#if LWIP_NETIF_HWADDRHINT
	i = find_entry(ipaddr, ETHARP_TRY_HARD, netif);
#else /* LWIP_NETIF_HWADDRHINT */
	i = find_entry(ipaddr, ETHARP_TRY_HARD);
#endif /* LWIP_NETIF_HWADDRHINT */

	/* could not find or create entry? */
	if(i < 0) {
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not create ARP entry\n"));

		if(q) {
			LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: packet dropped\n"));
			ETHARP_STATS_INC(etharp.memerr);
		}

		return (err_t)i;
	}

	/* mark a fresh entry as pending (we just sent a request) */
	if(arp_table[i].state == ETHARP_STATE_EMPTY) {
		arp_table[i].state = ETHARP_STATE_PENDING;
	}

	/* { i is either a STABLE or (new or existing) PENDING entry } */
	LWIP_ASSERT("arp_table[i].state == PENDING or STABLE",
	            ((arp_table[i].state == ETHARP_STATE_PENDING) ||
	             (arp_table[i].state == ETHARP_STATE_STABLE)));

	/* do we have a pending entry? or an implicit query request? */
	if((arp_table[i].state == ETHARP_STATE_PENDING) || (q == NULL)) {
		/* try to resolve it; send out ARP request */
		result = etharp_request(netif, ipaddr);

		if(result != ERR_OK) {
			/* ARP request couldn't be sent */
			/* We don't re-send arp request in etharp_tmr, but we still queue packets,
			   since this failure could be temporary, and the next packet calling
			   etharp_query again could lead to sending the queued packets. */
		}
	}

	/* packet given? */
	if(q != NULL) {
		/* stable entry? */
		if(arp_table[i].state == ETHARP_STATE_STABLE) {
			/* we have a valid IP->Ethernet address mapping */
			/* send the packet */
			result = etharp_send_ip(netif, q, srcaddr, &(arp_table[i].ethaddr));
			/* pending entry? (either just created or already pending */
		} else if(arp_table[i].state == ETHARP_STATE_PENDING) {
#if ARP_QUEUEING /* queue the given q packet */
			struct pbuf* p;
			int copy_needed = 0;
			/* IF q includes a PBUF_REF, PBUF_POOL or PBUF_RAM, we have no choice but
			 * to copy the whole queue into a new PBUF_RAM (see bug #11400)
			 * PBUF_ROMs can be left as they are, since ROM must not get changed. */
			p = q;

			while(p) {
				LWIP_ASSERT("no packet queues allowed!", (p->len != p->tot_len) || (p->next == 0));

				if(p->type != PBUF_ROM) {
					copy_needed = 1;
					break;
				}

				p = p->next;
			}

			if(copy_needed) {
				/* copy the whole packet into new pbufs */
				p = pbuf_alloc(PBUF_RAW, p->tot_len, PBUF_RAM);

				if(p != NULL) {
					if(pbuf_copy(p, q) != ERR_OK) {
						pbuf_free(p);
						p = NULL;
					}
				}
			} else {
				/* referencing the old pbuf is enough */
				p = q;
				pbuf_ref(p);
			}

			/* packet could be taken over? */
			if(p != NULL) {
				/* queue packet ... */
				struct etharp_q_entry* new_entry;
				/* allocate a new arp queue entry */
				new_entry = memp_malloc(MEMP_ARP_QUEUE);

				if(new_entry != NULL) {
					new_entry->next = 0;
					new_entry->p = p;

					if(arp_table[i].q != NULL) {
						/* queue was already existent, append the new entry to the end */
						struct etharp_q_entry* r;
						r = arp_table[i].q;

						while(r->next != NULL) {
							r = r->next;
						}

						r->next = new_entry;
					} else {
						/* queue did not exist, first item in queue */
						arp_table[i].q = new_entry;
					}

					LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: queued packet %p on ARP entry %"S16_F"\n", (void*)q, (s16_t)i));
					result = ERR_OK;
				} else {
					/* the pool MEMP_ARP_QUEUE is empty */
					pbuf_free(p);
					LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not queue a copy of PBUF_REF packet %p (out of memory)\n", (void*)q));
					/* { result == ERR_MEM } through initialization */
				}
			} else {
				ETHARP_STATS_INC(etharp.memerr);
				LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not queue a copy of PBUF_REF packet %p (out of memory)\n", (void*)q));
				/* { result == ERR_MEM } through initialization */
			}

#else /* ARP_QUEUEING == 0 */
			/* q && state == PENDING && ARP_QUEUEING == 0 => result = ERR_MEM */
			/* { result == ERR_MEM } through initialization */
			LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: Ethernet destination address unknown, queueing disabled, packet %p dropped\n", (void*)q));
#endif
		}
	}

	return result;
}

/**
 * Send a raw ARP packet (opcode and all addresses can be modified)
 *
 * @param netif the lwip network interface on which to send the ARP packet
 * @param ethsrc_addr the source MAC address for the ethernet header
 * @param ethdst_addr the destination MAC address for the ethernet header
 * @param hwsrc_addr the source MAC address for the ARP protocol header
 * @param ipsrc_addr the source IP address for the ARP protocol header
 * @param hwdst_addr the destination MAC address for the ARP protocol header
 * @param ipdst_addr the destination IP address for the ARP protocol header
 * @param opcode the type of the ARP packet
 * @return ERR_OK if the ARP packet has been sent
 *         ERR_MEM if the ARP packet couldn't be allocated
 *         any other err_t on failure
 */
#if !LWIP_AUTOIP
	static
#endif /* LWIP_AUTOIP */
err_t
etharp_raw(struct netif* netif, const struct eth_addr* ethsrc_addr,
           const struct eth_addr* ethdst_addr,
           const struct eth_addr* hwsrc_addr, const struct ip_addr* ipsrc_addr,
           const struct eth_addr* hwdst_addr, const struct ip_addr* ipdst_addr,
           const u16_t opcode)
{
	struct pbuf* p;
	err_t result = ERR_OK;
	u8_t k; /* ARP entry index */
	struct eth_hdr* ethhdr;
	struct etharp_hdr* hdr;
#if LWIP_AUTOIP
	const u8_t* ethdst_hwaddr;
#endif /* LWIP_AUTOIP */

	/* allocate a pbuf for the outgoing ARP request packet */
	p = pbuf_alloc(PBUF_RAW, SIZEOF_ETHARP_PACKET, PBUF_RAM);

	/* could allocate a pbuf for an ARP request? */
	if(p == NULL) {
		LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
		            ("etharp_raw: could not allocate pbuf for ARP request.\n"));
		ETHARP_STATS_INC(etharp.memerr);
		return ERR_MEM;
	}

	LWIP_ASSERT("check that first pbuf can hold struct etharp_hdr",
	            (p->len >= SIZEOF_ETHARP_PACKET));

	ethhdr = p->payload;
	hdr = (struct etharp_hdr*)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
	LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_raw: sending raw ARP packet.\n"));
	hdr->opcode = htons(opcode);

	LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
	            (netif->hwaddr_len == ETHARP_HWADDR_LEN));
	k = ETHARP_HWADDR_LEN;
#if LWIP_AUTOIP
	/* If we are using Link-Local, ARP packets must be broadcast on the
	 * link layer. (See RFC3927 Section 2.5) */
	ethdst_hwaddr = ((netif->autoip != NULL) && (netif->autoip->state != AUTOIP_STATE_OFF)) ? (u8_t*)(ethbroadcast.addr) : ethdst_addr->addr;
#endif /* LWIP_AUTOIP */

	/* Write MAC-Addresses (combined loop for both headers) */
	while(k > 0) {
		k--;
		/* Write the ARP MAC-Addresses */
		hdr->shwaddr.addr[k] = hwsrc_addr->addr[k];
		hdr->dhwaddr.addr[k] = hwdst_addr->addr[k];
		/* Write the Ethernet MAC-Addresses */
#if LWIP_AUTOIP
		ethhdr->dest.addr[k] = ethdst_hwaddr[k];
#else  /* LWIP_AUTOIP */
		ethhdr->dest.addr[k] = ethdst_addr->addr[k];
#endif /* LWIP_AUTOIP */
		ethhdr->src.addr[k]  = ethsrc_addr->addr[k];
	}

	hdr->sipaddr = *(struct ip_addr2*)ipsrc_addr;
	hdr->dipaddr = *(struct ip_addr2*)ipdst_addr;

	hdr->hwtype = htons(HWTYPE_ETHERNET);
	hdr->proto = htons(ETHTYPE_IP);
	/* set hwlen and protolen together */
	hdr->_hwlen_protolen = htons((ETHARP_HWADDR_LEN << 8) | sizeof(struct ip_addr));

	ethhdr->type = htons(ETHTYPE_ARP);
	/* send ARP query */
	result = netif->linkoutput(netif, p);
	ETHARP_STATS_INC(etharp.xmit);
	/* free ARP query packet */
	pbuf_free(p);
	p = NULL;
	/* could not allocate pbuf for ARP request */

	return result;
}

/**
 * Send an ARP request packet asking for ipaddr.
 *
 * @param netif the lwip network interface on which to send the request
 * @param ipaddr the IP address for which to ask
 * @return ERR_OK if the request has been sent
 *         ERR_MEM if the ARP packet couldn't be allocated
 *         any other err_t on failure
 */
err_t
etharp_request(struct netif* netif, struct ip_addr* ipaddr)
{
	LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_request: sending ARP request.\n"));
	return etharp_raw(netif, (struct eth_addr*)netif->hwaddr, &ethbroadcast,
	                  (struct eth_addr*)netif->hwaddr, &netif->ip_addr, &ethzero,
	                  ipaddr, ARP_REQUEST);
}

/**
 * Process received ethernet frames. Using this function instead of directly
 * calling ip_input and passing ARP frames through etharp in ethernetif_input,
 * the ARP cache is protected from concurrent access.
 *
 * @param p the recevied packet, p->payload pointing to the ethernet header
 * @param netif the network interface on which the packet was received
 */
err_t
ethernet_input(struct pbuf* p, struct netif* netif)
{
	struct eth_hdr* ethhdr;
	u16_t type;

	/* points to packet payload, which starts with an Ethernet header */
	ethhdr = p->payload;
	LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE,
	            ("ethernet_input: dest:%02x:%02x:%02x:%02x:%02x:%02x, src:%02x:%02x:%02x:%02x:%02x:%02x, type:%2hx\n",
	             (unsigned)ethhdr->dest.addr[0], (unsigned)ethhdr->dest.addr[1], (unsigned)ethhdr->dest.addr[2],
	             (unsigned)ethhdr->dest.addr[3], (unsigned)ethhdr->dest.addr[4], (unsigned)ethhdr->dest.addr[5],
	             (unsigned)ethhdr->src.addr[0], (unsigned)ethhdr->src.addr[1], (unsigned)ethhdr->src.addr[2],
	             (unsigned)ethhdr->src.addr[3], (unsigned)ethhdr->src.addr[4], (unsigned)ethhdr->src.addr[5],
	             (unsigned)htons(ethhdr->type)));

	type = htons(ethhdr->type);
#if ETHARP_SUPPORT_VLAN

	if(type == ETHTYPE_VLAN) {
		struct eth_vlan_hdr* vlan = (struct eth_vlan_hdr*)(((char*)ethhdr) + SIZEOF_ETH_HDR);
#ifdef ETHARP_VLAN_CHECK /* if not, allow all VLANs */

		if(VLAN_ID(vlan) != ETHARP_VLAN_CHECK) {
			/* silently ignore this packet: not for our VLAN */
			pbuf_free(p);
			return ERR_OK;
		}

#endif /* ETHARP_VLAN_CHECK */
		type = htons(vlan->tpid);
	}

#endif /* ETHARP_SUPPORT_VLAN */

	switch(type) {
		/* IP packet? */
		case ETHTYPE_IP:
#if ETHARP_TRUST_IP_MAC
			/* update ARP table */
			etharp_ip_input(netif, p);
#endif /* ETHARP_TRUST_IP_MAC */

			/* skip Ethernet header */
			if(pbuf_header(p, -(s16_t)SIZEOF_ETH_HDR)) {
				LWIP_ASSERT("Can't move over header in packet", 0);
				pbuf_free(p);
				p = NULL;
			} else {
				/* pass to IP layer */
				ip_input(p, netif);
			}

			break;

		case ETHTYPE_ARP:
			/* pass p to ARP module */
			etharp_arp_input(netif, (struct eth_addr*)(netif->hwaddr), p);
			break;

#if PPPOE_SUPPORT

		case ETHTYPE_PPPOEDISC: /* PPP Over Ethernet Discovery Stage */
			pppoe_disc_input(netif, p);
			break;

		case ETHTYPE_PPPOE: /* PPP Over Ethernet Session Stage */
			pppoe_data_input(netif, p);
			break;
#endif /* PPPOE_SUPPORT */

		default:
			ETHARP_STATS_INC(etharp.proterr);
			ETHARP_STATS_INC(etharp.drop);
			pbuf_free(p);
			p = NULL;
			break;
	}

	/* This means the pbuf is freed or consumed,
	   so the caller doesn't have to free it again */
	return ERR_OK;
}
#endif /* LWIP_ARP */
